Hi Ruediger, thanks for your questions. Well, some of the questions I can answer already:
Branding: It's the typical Vodafone skin, nothing dramatic and it can be changed to anything else. Thankfully it's not hardcoded. So you can either use the original Windows Mobile skins or download/create 3rd party skins.
Stereo Quality: That's always hard for me to figure out. Personally I'm only using stereo Bluetooth headsets for convenience, especially because you can use this headsets for calls and listening music. Due to this fact, the quality is reduced already. Also I don't have any mini USB to 3.5 mm adapters here (but they are available from HTC) to use any of the better headsets I have.
Mass Storage: Don't think so (AFAIK it's still not supported under Window Mobile 6) but I have to test.
But I will test and express my impression in the review. If you have further comments,please let me know.